信沖洞坐(zuo)落在混(hun)雅嶺南(nan)部(bu)懸崖峭壁上(shang),海拔高近60米。昌(chang)化江(jiang)(jiang)支(zhi)流南(nan)陽溪自東向西流經洞口下方,西距昌(chang)化江(jiang)(jiang)僅約1公里。入選第(di)七批全國重點文(wen)物(wu)保護單(dan)位名(ming)單(dan)。
信(xin)沖洞(dong)距南(nan)陽溪河(he)面高約20米(mi),其地質結構較為復雜,因(yin)長(chang)年雨水侵(qin)蝕,石灰(hui)巖(yan)山體形成(cheng)了洞(dong)中有洞(dong)的地貌特點。
洞(dong)(dong)(dong)(dong)底斜著向上(shang)(shang)、向后延伸,洞(dong)(dong)(dong)(dong)的(de)后壁(bi)和洞(dong)(dong)(dong)(dong)頂(ding)呈弧狀連成(cheng)一片,洞(dong)(dong)(dong)(dong)底上(shang)(shang)部和下部各形成(cheng)一個小平臺,洞(dong)(dong)(dong)(dong)的(de)上(shang)(shang)部至洞(dong)(dong)(dong)(dong)頂(ding)則為(wei)一條很長的(de)裂隙。此外,在洞(dong)(dong)(dong)(dong)內東(dong)壁(bi)還有(you)3個小支洞(dong)(dong)(dong)(dong)。主洞(dong)(dong)(dong)(dong)口(kou)(kou)高約15米(mi),小支洞(dong)(dong)(dong)(dong)口(kou)(kou)高約2—2.5米(mi)。
信沖洞(dong)(dong)(dong)遺址是(shi)跨越數十(shi)萬年(nian)的文化(hua)遺產(chan),是(shi)珍稀資源、旅游資源和科學(xue)研(yan)究(jiu)(jiu)資源。在洞(dong)(dong)(dong)頂(ding)的裂隙堆和幾個支(zhi)洞(dong)(dong)(dong)中(zhong)發現動(dong)物化(hua)石,其中(zhong)包括靈長目(mu)(mu)、食肉目(mu)(mu)、長鼻目(mu)(mu)、奇蹄目(mu)(mu)、偶蹄目(mu)(mu)、嚙齒目(mu)(mu)、爬行目(mu)(mu)及(ji)鳥(niao)類、魚類等,主要有巨猿、象、中(zhong)國(guo)(guo)犀、最(zui)后鬣(lie)狗和牛、鹿(lu)、野豬、豪豬、貘(mo)、鼠等哺乳動(dong)物化(hua)石,其中(zhong)有些動(dong)物屬于滅絕種。經(jing)中(zhong)國(guo)(guo)地(di)震局地(di)質研(yan)究(jiu)(jiu)所地(di)震動(dong)力學(xue)國(guo)(guo)家重點實驗室(shi)電(dian)子自旋共振(ESR)法測定(ding),信沖洞(dong)(dong)(dong)動(dong)物化(hua)石年(nian)代(dai)距(ju)今40萬年(nian),洞(dong)(dong)(dong)穴內堆積地(di)質時代(dai)為(wei)更新世(shi)中(zhong)期。
信沖洞(dong)遺址是目前我國南部(bu)的(de)一(yi)(yi)處古生(sheng)物(wu)化石地(di)點,對進一(yi)(yi)步了(le)解我國古生(sheng)物(wu)化石的(de)分(fen)布范圍和種(zhong)類具有一(yi)(yi)定意義,對探討海(hai)南古氣候、古環境、古地(di)理變遷(qian)及第(di)四紀(ji)地(di)層學提供新的(de)實物(wu)資(zi)料。尤其(qi)是巨猿牙齒化石的(de)發(fa)現,為尋找(zhao)海(hai)南古人類和舊(jiu)石器時代考古文化提供了(le)重要(yao)的(de)信息。
據中(zhong)(zhong)國科學院(yuan)古脊(ji)椎動(dong)物(wu)與古人類(lei)研究所:古脊(ji)椎所李錄、佟海(hai)(hai)燕,廣西自(zi)然(ran)博物(wu)館莫進尤和海(hai)(hai)南昌(chang)江博物(wu)館黃兆(zhao)雪描述了(le)一件產(chan)自(zi)海(hai)(hai)南昌(chang)江黎族自(zi)治縣信(xin)沖洞洞穴沉(chen)積(ji)中(zhong)(zhong)的(de)龜(gui)(gui)鱉(bie)(bie)類(lei)化(hua)石——中(zhong)(zhong)華(hua)花(hua)龜(gui)(gui),這是關于海(hai)(hai)南龜(gui)(gui)鱉(bie)(bie)類(lei)化(hua)石的(de)首(shou)次報道,論(lun)文應邀發表在泰國馬(ma)哈沙拉堪(kan)大學學報《Research & Knowledge》創刊號上。中(zhong)(zhong)華(hua)花(hua)龜(gui)(gui)的(de)發現(xian)不僅填(tian)補(bu)了(le)海(hai)(hai)南島龜(gui)(gui)鱉(bie)(bie)化(hua)石分布的(de)空(kong)白,也為(wei)中(zhong)(zhong)國現(xian)生龜(gui)(gui)鱉(bie)(bie)類(lei)分布格局的(de)形成提供了(le)重(zhong)要信(xin)息。
信(xin)沖洞(dong)(dong)位于昌(chang)(chang)(chang)江(jiang)(jiang)黎族自(zi)治縣縣城南(nan)(nan)(nan)20公里處(chu),昌(chang)(chang)(chang)江(jiang)(jiang)支流南(nan)(nan)(nan)陽溪右岸,洞(dong)(dong)口距水面20米。1995年,信(xin)沖洞(dong)(dong)脊椎動(dong)物(wu)化(hua)石首(shou)次(ci)被當地村民發現(xian)(xian),2006年經海(hai)南(nan)(nan)(nan)文體廳(ting)、海(hai)南(nan)(nan)(nan)文物(wu)考(kao)古研(yan)究(jiu)所、中(zhong)(zhong)科院古脊椎所和昌(chang)(chang)(chang)江(jiang)(jiang)縣博物(wu)館聯合發掘,共(gong)發現(xian)(xian)包(bao)括巨猿、劍齒(chi)象、中(zhong)(zhong)國犀、鬣(lie)狗、碩(shuo)豪(hao)豬等在內的近20種哺(bu)乳動(dong)物(wu)化(hua)石和若干其他(ta)類群化(hua)石。據(ju)電子自(zi)旋(xuan)共(gong)振法測定,信(xin)沖洞(dong)(dong)洞(dong)(dong)穴(xue)沉積物(wu)形成年代距今約40萬年,屬中(zhong)(zhong)更(geng)新世。但(dan)這件龜鱉(bie)類化(hua)石一直(zhi)未被報道,直(zhi)到論文第二(er)作者(zhe)莫進尤在參(can)觀(guan)昌(chang)(chang)(chang)江(jiang)(jiang)博物(wu)館時重新發現(xian)(xian)。
該化石保(bao)存了較完(wan)整的甲(jia)(jia)殼后(hou)半部,屬于(yu)地(di)龜(gui)科擬(ni)水(shui)龜(gui)屬,具有(you)以(yi)下鑒定特征(zheng):背(bei)甲(jia)(jia)隆起程(cheng)度中(zhong)等(deng),側(ce)背(bei)脊成年(nian)后(hou)消失;具兩枚上臀板和(he)(he)一枚臀板;除第(di)12對(dui)緣盾,所有(you)緣盾溝(gou)均位于(yu)緣板縫外側(ce),在第(di)6、7對(dui)緣盾處溝(gou)和(he)(he)縫十(shi)分接(jie)近;第(di)12對(dui)緣盾間(jian)溝(gou)垂直穿插(cha)第(di)2上臀板和(he)(he)臀板間(jian)骨縫。中(zhong)華花(hua)(hua)龜(gui)是一種現(xian)生淡(dan)水(shui)龜(gui)類,廣泛分布(bu)于(yu)中(zhong)國華南(nan)地(di)區以(yi)及(ji)老撾、越(yue)南(nan)。中(zhong)華花(hua)(hua)龜(gui)曾發現(xian)于(yu)山西(xi)上新世地(di)層(ceng),澎(peng)湖列島海底更新世地(di)層(ceng)及(ji)河南(nan)殷(yin)墟(xu)商代(dai)遺址。
海(hai)(hai)南(nan)(nan)(nan)島(dao)地(di)處(chu)熱帶北緣(yuan),屬熱帶季風(feng)氣候,很適宜(yi)兩棲(qi)爬行動物繁衍生(sheng)存。得益于此,海(hai)(hai)南(nan)(nan)(nan)島(dao)是中(zhong)國現(xian)(xian)生(sheng)龜(gui)(gui)鱉(bie)類(lei)豐(feng)富的地(di)區之一,擁(yong)有(you)中(zhong)國龜(gui)(gui)鱉(bie)類(lei)所有(you)科(ke)(ke)(ke)級分(fen)類(lei)單元,包括海(hai)(hai)龜(gui)(gui)科(ke)(ke)(ke)、棱(leng)皮龜(gui)(gui)科(ke)(ke)(ke)、鱉(bie)科(ke)(ke)(ke)、地(di)龜(gui)(gui)科(ke)(ke)(ke)、平胸(xiong)龜(gui)(gui)科(ke)(ke)(ke)和(he)陸(lu)龜(gui)(gui)科(ke)(ke)(ke)。其中(zhong),所有(you)的海(hai)(hai)生(sheng)龜(gui)(gui)鱉(bie)類(lei)和(he)至少十一種非海(hai)(hai)生(sheng)龜(gui)(gui)鱉(bie)類(lei)在海(hai)(hai)南(nan)(nan)(nan)島(dao)均有(you)分(fen)布。但同(tong)樣(yang)由于環境因(yin)素和(he)地(di)質歷(li)史因(yin)素,海(hai)(hai)南(nan)(nan)(nan)島(dao)的脊(ji)椎(zhui)動物化石較稀少,之前(qian)從未發現(xian)(xian)過龜(gui)(gui)鱉(bie)類(lei)化石。
據研(yan)究人(ren)員介紹,中(zhong)(zhong)華(hua)花(hua)龜是一種淡水龜類,其(qi)何(he)時、以何(he)種方(fang)式通過瓊(qiong)州海(hai)峽(xia)或是在瓊(qiong)州海(hai)峽(xia)形成前已經到達海(hai)南(nan)(nan)(nan)島(dao),這(zhe)一問題值得進一步(bu)研(yan)究。研(yan)究人(ren)員相(xiang)信此次海(hai)南(nan)(nan)(nan)島(dao)距今40萬年中(zhong)(zhong)華(hua)花(hua)龜化石(shi)的發現為瓊(qiong)州海(hai)峽(xia)形成年代乃至南(nan)(nan)(nan)海(hai)更(geng)新世海(hai)平面變化的研(yan)究積累了珍(zhen)貴材(cai)料。