* Dubai's Arabtec corrects after Wednesday's surge
* Abu Dhabi's TAQA jumps on possible U.S. asset sales
* Qatar's Gulf International Services slumps on weak Q1
* Saudi is worst-performing index for the week
* Egypt's Orascom Construction up on new U.S. facility
By Celine Aswad
DUBAI, April 20 (Reuters) - Profit-taking and weak first-quarter earnings weighed on Gulf stock markets on Thursday, with Saudi Arabia's index pulled lower by petrochemical shares after oil prices fell sharply, but Dubai's Union Properties and Abu Dhabi's TAQA bucked the trend.
Dubai's index lost 1.0 percent as financially troubled builder Arabtec, which had jumped almost 11 percent on Wednesday after shareholders approved its capital restructuring plan, retreated 4.4 percent.
Union Properties, however, leapt 5.8 percent to close at 1.03 dirhams in its heaviest trade since Jan. 23 and accounted for almost half of trading volume on the exchange. It ended off its intra-day high of 1.12 dirhams, failing to conclusively break chart resistance at the end-February peak of 1.07.
Fund managers and traders said the reason for the jump was not clear but it could be related to positive corporate news that had not yet been disclosed.
"Shares of UPP moved against the grain, and if it was just market participants taking a contrarian view on the stock, it would happen gradually. The volume spike in today's session suggests it's a company-specific event," one fund manager said.
Elsewhere, Abu Dhabi National Energy Co surged 7.1 percent in very heavy trade after its chief operating officer told Reuters it might sell some oil and gas interests in North America to raise capital for core businesses.
Profit-taking in other shares, however, pulled the Abu Dhabi index down 0.2 percent. First Abu Dhabi Bank fell 0.5 percent after trading as much as 1.4 percent higher earlier in the day.
The lender, which was formed on April 1 by the merger of National Bank of Abu Dhabi and First Gulf Bank, announced a 12.4 percent rise in combined "pro-forma" first quarter net profit to 2.93 billion dirhams ($798 million).
That was aided by a 145.5 percent jump in "other non-interest" income while loan impairment charges slipped 3.9 percent.
The Saudi index lost 0.7 percent as almost two-thirds of listed petrochemical shares fell, with heavyweight Saudi Basic Industries dropping 1.3 percent.
Most Saudi banking shares also fell, with Saudi Investment Bank the worst performer, down 1.6 percent. All Saudi banks have now reported first-quarter earnings; while results were mixed, most beat analysts' expectations.
The Saudi index was the worst performer in the Gulf for the week, down 2.5 percent.
In Doha, Gulf International Services dropped 5.0 percent after it reported an 81 percent slide in first-quarter profit to 15 million riyals ($4.1 million), far below QNB Financial's forecast of 452 million riyals and Alphamena's estimate of 378 million riyals.
The Qatari stock index fell 0.5 percent and was down 2.0 percent for the week.
In Egypt, the index edged up 0.1 percent in very low volume as Orascom Construction jumped 5.1 percent on news a major U.S. nitrogen fertiliser plant which it built had started operations.
Declining shares, however, outnumbered advancing ones by 124 to 46.
* The index lost 0.7 percent to 6,899 points.
* The index fell 1.0 percent to 3,470 points.
* The index edged down 0.2 percent at 4,522 points.
* The index lost 0.5 percent to 10,242 points.
* The index edged up 0.1 percent to 12,906 points.
* The index added 0.4 percent to 6,814 points.
* The index slipped 0.7 percent to 5,474 points.
* The index was down 0.4 percent at 1,334 points.
Editing by Andrew Torchia and Mark Potter